The invention relates to a sensor for determining at least one parameter and a sigma-delta converter.
Sensors of this type usually posses a measuring cell generating an analog voltage signal. The voltage signal is fed to a sigma-delta converter for being converted to a digital signal.
Sigma-delta converters are circuits by means of which analog signals can be converted into digital signals. They usually comprise an amplifier with feedback capacitor and input capacitors and a comparator as well as switches for switching the various capacitors with a given clock and depending on the comparator. The output signal of the comparator can be evaluated statistically by being fed to a filter, e.g. a counter. The number of pulses per time unit determined by the counter are, in most of the embodiments of such converters, proportional to the input voltage.
Usually, one of the input capacitors is connected via a first switch to the voltage to be measured, and a second one of the input capacitors is connected via a second switch to a reference voltage. By suitable operation of the converter these two voltages can be compared to each other in quantitative manner.
In order to obtain an accuracy as high as possible, sigma-delta converters are often built symmetrically and have two separated amplifier channels. Each amplifier channel has its own feedback capacitor and its own input capacitors, and the channels are being switched oppositely. The comparator compares the signals of both channels.